This invention is concerned with a drug delivery system primarily intended for, but not limited to, use in an environment which is normally low in available body fluid volume such as the rectal or vaginal cavity. The novel design is particularly suitable for its intended use inasmuch as the water necessary for dissolution of the active ingredients is provided as an integral part of the novel drug delivery system.
Drug delivery systems carrying their own water are known in the art and one such device is disclosed in Austral. J. Exp. Biol., 33, 415 to 420, (1955). This device consists of three compartments confined in a specifically constructed housing and a clamp to hold a semi-permeable membrane. The driving force of the device depends on the continual presence of a solution of an osmotically effective red dye solute that exhibits an osmotic pressure gradient against water. The red dye is contained in a partially collapsed rubber compartment and it is separated from a second compartment containing water by a semi-permeable membrane. The partially collapsed bag is housed in a glass ampoule, along with a product compartment defined by the space between the bag and one end of the glass ampoule. The distant end of the ampoule defines a water compartment. The ampoule also is provided with a drug release nipple, and in operation when the product compartment is charged with a solution of a product, water in the water compartment moves through the semi-permeable membrane into the dye solution increasing its volume in the compartment causing it to expand against the rubber providing the mechanical force necessary to eject the product solution through the nipple. It is immediately evident that this device has certain adverse features that tend to diminish its practical use. For example, the device is difficult to construct into compartments that are essentially free of leaks and because of the fabrication demands of a movable material that necessitates a rigid outer housing. Another inherent disadvantage which prevented its wide acceptance by the medical community is the requirement that the drug be in solution. Such solutions tend to be released from the device by simple leaching; they do not permit high concentrations of the product to be embodied within the device; they often promote chemical deterioration of the active drug; and they do not permit the use of insoluble or poorly soluble drugs.
It is an object of this invention to provide a drug delivery system comprising a core of aqueous solubulizing system in a wax housing which melts at body temperature surrounded by a matrix of drug and water dispersible excipients which may also be coated with a semi-permeable membrane to modulate release of drug solution.
It is a further object of this invention to provide such a system primarily for use in an environment low in body fluid volume such as the rectal cavity.
It is also an object of this invention to provide a novel drug delivery system that is simple and easy to construct, that carries its own water, and in which the drug is in solution only after administration of the device.